World's most polluted cities

Severe pollution is once again choking Shanghai and other cities in China, disrupting hundreds of flights and forcing schools to close. China is home to some of the world's most polluted cities -- take a look at some of the others.

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Bhopal, India -- In December 1984, a toxic gas leak at a local pesticide plant that killed nearly 4,000 people outright, rising to 15,000 in the coming week in one of the world's worst industrial disasters. Even now, thousands in Bhopal suffer and die from chronic illnesses largely due to contaminated groundwater.